This invention relates to a spherical bonded abrasive and a process for its production. More particularly, it relates to hollow spherical bonded abrasives comprising a thermoplastic support onto the periphery of which is bonded abrasive granules.
Many abrasive operations with coated abrasives attain an incomplete utilization of the abrasive grain, due to the grain configuration. The typical abrasive grain fragmentation with edge renewal occurs in mechanically stable bonds customarily down to the height of the base adhesive coat. Due to the strong encasement of the remaining grain a renewal of the edge is no more possible. Weaker embedding of grains usually leads to complete grain break out at higher working pressure. Moreover, the high scratch depth attained during initial grinding decreases relatively quickly and in addition the efficiency of the grinding belt diminishes.
According to the present state of the art there existed already assessments to arrive at a better solution during surface machining through a different abrasive grain arrangement. Thus for example it was proposed to deposit and to bond abrasive grain on a carrier material loaded beforehand with cork chips. A coated abrasive, produced in such a manner, has the advantage of a larger abrasive grain potential per unit of area, whereas of course it had to put up with a smaller scratch depth due to a relatively soft cork backing.
A process for the production of bonded abrasive with porous grain is described in German Pat. No. 939,377. This process is characterized by wetting high melting oxides, in particular aluminum oxide, by transforming them through gas evolution with the help of hydrogen peroxide, and subsequent burning into porous single grains.
German patent application (Offenlegungsschrift) No. 2,425,887 describes the production and utilization of spherically encapsulated abrasive grains whereby the utilization is limited to polishing and lapping due to the special bond of the encapsulated abrasive grain. The abrasive grain is loosely embedded in the auxiliary grinding material (e.g., carnauba wax) and by encasing it for example in ureaformaldehyde it is transformed into spherical or ellipsoidal shape.
To improve the grinding process it was likewise proposed to use hollow spheroidal bonded abrasives together with conventional abrasive grain. Through the hollow spheroidal abrasive grain the porosity ought to be increased in order to make cooler grinding possible. For steel grinding the total fraction of hollow spheroidal abrasive shall not amont to more than 10% by weight in relation to the conventional abrasive grain. To increase the proportion in hollow spheroidal abrasive grain it was proposed in German patent application (Offenlegungsschrift) No. 2,349,326 to mix hollow unbroken bonded abrasives with splintery broken, cup-like bonded abrasives.